This invention relates generally to mattress foundation structures and more particularly to a box spring assembly of the type which utilizes non-coil springs. Box spring assemblies of this general type have been known since 1964, the first of such spring assemblies being disclosed in U.S. Pat. No. 3,286,281. Subsequently issued patents disclosing the same general type of box spring assembly are: U.S. Pat. Nos. 3,487,480; 3,506,987; 3,574,240; 3,574,241; 3,665,529; 3,680,157; 3,755,833; 3,824,639; 3,852,838; 4,060,862; 4,120,058; 4,131,961; 4,195,376; 4,218,790; 4,238,861; 4,251,892; 4,253,208; 4,339,834; 4,398,705, and 4,470,584.
Box spring assemblies of the general type shown in the above list of patents, all of which are owned by the assignee of this application, are advantageous with respect to the conventional box spring assemblies using coil springs because they provide a desired stiffer foundation for the mattress and contain a reduced amount of wire. These box spring assemblies are also advantageous from the standpoint of prolonged service life, ease of assembly and cost of manufacture. Additional box spring assemblies of this general type are shown in U.S. Pat. Nos. 3,546,723; 3,596,299; 3,722,013; 3,825,960; 3,833,948; 3,835,485; 3,869,740; 3,990,121; and 4,000,531.
Some current box spring assemblies typically have a wire grid assembly which is supported by an array of springs attached to a supporting frame. One approach of reducing the cost of the box spring assembly is to minimize the gauge of the wires making up the grid assembly. Grid assembly wire diameter, however, is dependent upon the characteristics of the spring units on which the grid is supported. Some spring unit types do not distribute their loads evenly over the grid assembly but instead exert undesirable localized or point loads which tend to permanently deform portions of the grid assembly when it is subjected to bedding loads.
A spring module which reduces the localized loading on the grid assembly formed from wire having a reduced diameter is shown and described in U.S. Pat. No. 4,739,977, owned by the assignee of the present invention. This patent discloses an improved spring for box spring assembly in which the springs provide self limited deflection to prevent them from taking on a permanent set after being overloaded and the top portion of the spring spreads out forces over a large area on the grid to reduce point loading. This allows use of grid wire of a reduced diameter or higher gauge.
Another aspect which effects the cost of production of spring unit of a box spring assembly is the number of individual component parts. For example, the box spring assembly as disclosed by the patent above includes a frame, a wire grid, various deck support spring units, and a plurality of clips which are used to secure the springs to the wire grid. Placement of the wire grid on the springs requires the separate steps of placing these clips and of crimping these clips around the wires of the spring unit and the wire grid members. The separate application of these clips adds steps which affect the overall cost of construction of the box spring assembly.
U.S. Pat. No. 4,339,834 discloses a support spring module of the limited deflection type which is designed to interlock with the intersecting wire deck members of a box spring assembly without the use of clips. Each spring interlocks with a single intersection of criss-crossed wire deck members. Therefore, a spring is associated with each intersection in the wire grid.
The spring interlocking with the crossed wires at the intersection creates a stack of wires at the intersection three wires diameters high creating an undesirably high hump at each intersection rather than maintaining a flat deck surface. It is desirable to minimize the stacking of wires at the intersection to maintain a generally flat wire deck surface.
U.S. Pat. No. 4,398,705 discloses a support spring module identical to that disclosed in U.S. Pat. No. 4,339,834 used with a welded wire grid. Once again, this assembly has the disadvantage that each intersection of wire gird members requires a single support spring interlocked with the intersecting grid wire members at the intersection.
It is therefore an object of the present invention to provide a box spring assembly which requires no fasteners to lock the deck support to the deck wire grid.
It is another object of the present invention to provide a box spring assembly wherein the installation of each deck support spring locks the intersecting grid wires forming a pair of spaced intersections in place with respect to each other and the spring.
It is another object of the present invention to provide an interlocked spring and wire grid assembly that prevents shifting of the wire grid members and springs.
It is another object of the present invention to provide a box spring assembly wherein the thickness at the intersections between the deck support springs and the grid members are only two wire diameters to maintain a flat support deck.
It is a further object of the present invention to provide a box spring assembly wherein the force holding the long wires of the wire grid in place is provided by the deck support springs.
A box spring assembly according to the present invention includes a generally rectangular frame, a mattress support deck disposed a predetermined distance above the frame, and a plurality of deck support springs arranged between the deck and the frame so as to yieldably support the deck on the frame. The deck is made up of a plurality of criss-crossed wire deck members having spaced notches. These notches are engaged at or adjacent the intersection of the wire members and thus coact to maintain the wire deck members in the criss-crossed configuration forming a wire grid. The ends of the criss-crossed deck wire members are attached to a border wire which forms the perimeter of the mattress support deck.
The deck support springs arranged between the deck and frame to yieldably support the deck on the frame each has a vertical yieldable portion mounted to the frame at one end, and terminating at the other end in a deck attaching portion. The deck attaching portion includes a pair of straight end wire sections arranged in a side-by-side parallel relation. The end straight wire sections are interlocked with a spaced pair of intersections of the deck wire members to lock the deck wire members and the spring together at the notches in the deck support springs adjacent the notched intersections of the deck wire members.
Further benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims taken in conjunction with the accompanying drawings.